Currents

Question 1

what are the four ways in which ions can move between action potentials?

Answer 1

1. Na+, K+, Cl- leak channels (2P K+)
2. hyperpolarization-activated voltage-gated channels (HCN)
3. some voltage-gated channels (inward rectifier K+)
4. slow-inactivating channels that are still open (KV2.1)
   (A- are always trapped)

Question 2

which factors determine the membrane potential?

Answer 2

differential membrane permeability, concentration gradient, electrostatic pressure, active transporters

Question 3

how are ions able to cross the semi-permeable membrane?

Answer 3

through leak and voltage-gated slow/non-inactivating channels

Question 4

how does electrostatic pressure determine the membrane potential?

Answer 4

opposite-polarity molecules attract allowing them to cross membrane, same-polarity molecules repel each other, meaning they will cross the membrane to avoid each other

Question 5

what is the equilibrium potential of an ion?

Answer 5

the membrane potential at which that ion is at rest, when it alone can move because the concentration gradient and the electrostatic pressure are balanced out

Question 6

how can you determine which current will be the strongest and what direction it will move in?

Answer 6

ions that are oppositely charged from the membrane potential will flow inward, ions of the same charge will flow outwards, the ion with the largest different between it and the membrane potential will have the strongest current

Question 7

why is the resting membrane potential not just the average of all electric potentials?

Answer 7

because the semi-permeability of the membrane and the leak channels within it allow ions to constantly move across the membrane and alter the membrane potential, and because there are more K+ and Cl- leak channels than Na+ they will not line up

Question 8

why do glia have really negative resting membrane potential?

Answer 8

because they contain only K+ leak channels which allows K+ to leave, making the inside more negative, lowering the resting membrane potential

Question 9

what are local potentials?

Answer 9

membrane potentials changes elicited by receptor stimulation

Question 10

what do EPSPs do?

Answer 10

excitatory postsynaptic potentials attach to dendritic spine heads and depolarize the cell (make it less negative), decreasing the membrane potential and increasing the likelihood of an action potential occurring

Question 11

what do IPSPs do?

Answer 11

inhibitory postsynaptic potentials attach to dendritic spine shafts and hyperpolarize the cell (make it more negative), increasing the membrane potential and decreasing the likelihood of an action potential occurring

Question 12

how does the placement of different types of channels influence if an action potential will occur or not?

Answer 12

KV4.2 channels are located on the distal ends of neurons, since they are fast gating K+ channels they can detect local IPSPs and EPSPs
KV2.1 channels are located on the proximal ends of neurons, since they are slow gating K+ channels they allow a lot of K+ to leave the cell, this lowers to likelihood of an action potential and hold membrane potential down by remaining open, meaning that only strong currents will result in an action potential

Question 13

what are graded potentials?

Answer 13

action potentials that slowly decline in size over time

Question 14

what factors can influence the rate of decrement?

Answer 14

membrane capacitance, membrane conductance, and intracellular resistance
summation/integration for local potentials

Question 15

what is membrane capacitance and how does it influence the rate of decrement?

Answer 15

ability to retain charge/separate ions, leak channels allow ions to leak out which decreases the intensity of the signal, low capacitance correlates to a very leaky membrane, high capacitance correlates to few leak channels

Question 16

what is membrane conductance and how does it influence the rate of decrement?

Answer 16

the efficiency of conducting current, how many ions travel, changes in membrane potential influence when gates open, how long specific channels stay open, and blockers all influence conductance

Question 17

what is intracellular resistance and how does it influence the rate of decrement?

Answer 17

anything impeding the flow of ions, properties of the cytoplasm, neurite length and diameter both influence intracellular resistance

Question 18

what is integration and how does it influence the rate of decrement?

Answer 18

when local potentials (EPSPs/IPSPs) combine signals or cancel each other out, same charges combine and amplify and opposite charges cancel each other out

Question 19

why does integration of local potentials and creation of action potentials occur at the axon hillock?

Answer 19

because a lot of voltage gated Na+ channels that can start an action potential appear at the axon hillock, also contains special K+ channels that open faster to repolarize the cell

Question 20

what are the two types of integration?

Answer 20

spatial summation and temporal summation

Question 21

what is spatial summation?

Answer 21

the idea that IPSPs and EPSPs that arrive simultaneously from different synapses sum together or cancel each other out

Question 22

what is temporal summation?

Answer 22

the idea that EPSPs or IPSPs that arrive from the same synapse in rapid succession will sum the together, they cannot cancel each other out because they come from the same synapse and will therefore have the same charge